Tempos intensamente gelados para os dinossauros: evidência de queda brusca de temperatura no Cretáceo

quinta-feira, setembro 16, 2010

Frosty Times for Dinosaurs: Major Fall in Temperature 137 Million Years Ago During Cretaceous Greenhouse Period, Evidence Shows

ScienceDaily (Sep. 15, 2010) — A major drop in temperature 137 million years ago briefly interrupted the warm, equable climate of the Cretaceous Period. The water temperature in the Arctic Ocean fell from around 13°C to between 4 and 7°C, possibly causing the poles to freeze over.

An ammonite used to resolve the biostratigraphy of the successions. (Credit: Photo by Elizabeth V. Nunn)

Gregory Price from the University of Plymouth, UK and Elizabeth Nunn from Johannes Gutenberg University Mainz, Germany investigated rock samples with fossil belemnites and glendonites from Svalbard in order to determine the temperature of the Arctic Ocean between 140 and 136 million years ago. Such paleoclimate reconstructions help to improve predictions for future climate and environmental development and to gauge the impact of the human race on climate. The temperature of the oceans plays an important role in the history of the Earth's climate.

Current findings indicate that the global climate during the Cretaceous Period was warm and equable with high atmospheric CO2 values, although scientists have already speculated that this global warmth may have been punctuated by colder episodes.

The latest research carried out by Price and Nunn shows that there was a brief cold episode approximately 137 million years ago. "Temperatures fell drastically compared with the average water temperatures of 13°C or even 20°C in the Arctic region during the rest of the Cretaceous Period," states Nunn. Dinosaurs inhabited the polar regions during the Cretaceous greenhouse period. While marine reptiles such as pliosaurs and ichthyosaurs may have migrated with the onset of the cold snap, it is not clear how dinosaurs would have handled the colder conditions.

Read more here/Leia mais aqui: Science Daily


Valanginian isotope variation in glendonites and belemnites from Arctic Svalbard: Transient glacial temperatures during the Cretaceous greenhouse

Gregory D. Price1 and Elizabeth V. Nunn2

-Author Affiliations

1School of Geography, Earth and Environmental Sciences, University of Plymouth, Drake Circus, Plymouth PL4 8AA, UK
2Department of Applied and Analytical Paleontology, Institute for Geosciences, Johannes Gutenberg-Universität Mainz, Johann-Joachim-Becher-Weg 21, 55128 Mainz, Germany


Oxygen and carbon isotope data from Cretaceous (Valanginian) glendonites and belemnites from Arctic Svalbard are presented. Oxygen isotope data from well-preserved glendonites, in conjunction with the ikaite to glendonite pseudomorph transition temperature, are used to provide an estimate of the oxygen isotope composition of ambient seawater. Calculation of such a factor is essential for robust paleotemperature estimates. Using this methodology, our paleotemperatures calculated from the oxygen isotope compositions of coexisting belemnites yield cool temperatures (4–7 °C) consistent with transient glacial polar conditions during the Cretaceous greenhouse. Cool polar temperatures during the Cretaceous help reconcile geologic data with the simulations of general circulation models. Nevertheless, beyond this postulated and transient cool event within the Valanginian, the remainder of the isotope data are interpretable in terms of warm polar conditions during the Cretaceous greenhouse.

Received 5 August 2009.
Revision received 1 October 2009.
Accepted 6 October 2009.
© 2010 Geological Society of America